Crankcase of bicycle frame



Feb. 23, 1954 L. sHAKEsBY ET AL CRANKCASE OF BICYCLE FRAME Fi'led June 42e. 1951 LEONARD SHA/(E557 SAINSBLY wtjs F REDER/CK L Patented Feb. 23,r 1954 CRANKCASE F BICYCLE FRAME Leonard Shakesby and Frederick L. Sainsbury,

Weston, Cycle and Motor Ontario, Canada Ontario, Canada, assignors to Canada Company Limited, Weston,

Application June 26, 1951, Serial No. 233,530

2 claims. (ci. 28o-281) This invention relates generally to bicycles and more specically to the formation of the crank case of a bicycle.

In the conventional bicycle a pedal crank having two crank arms joined by a connecting shaft is journalled within a crank case on a bicycle frame. In the past, two types of cranks have been popular, one, the one piece crank, and, two, the three piece crank. The one piece crank comprises two crank arms with their longitudinal axes in parallel spaced relation and united at their inner ends by a connecting shaft portion. In the three piece crank, the crank arms are formed separately to the connecting portion and are joined to it by means of pins.

Each type of crank has its advantages and disadvantages. The one piece crank, is, of course, the cheaper to make and generally speaking stronger because no pinned joints are involved, but the crank case in which it is journalled must be made relatively large to accommodate the sweep of the elbow formed Where the crank arm unites with the connecting shaft portion as it is projected into the tubular crank case.

With the three piece crank, the crank case can be made with a relatively small diameter'because it is only necessary to project astraight connecting portion through it when assembling the bicycle. The crank arms are pinned to the connecting portion after it has been journalled in the crank case.

We have devised a crank case, the general diameter of which is substantially the same as the diameter of the crank case that accommodates a three piece crank, but which is capable of mounting a conventional one piece crank as well as a three piece crank. With our construction the required diameter of the crank case for both the one piece and the three piece crank is substantially the same size and bicycle manufacture and service is considerably more standardized. It is also cheaper to form a crank case with a smaller diameter.

It is, then, a prime object of our invention to form a bicycle crank case of relatively small diameter in which can be mounted both a one piece and a three piece crank.

Other objects of our invention will be apparent from reading the disclosure.

Generally speaking, our improved crank case has a cross-section too small to accommodate the sweep of the elbow formed where crank arms and the connecting shafts of a one piece crank unite as the crank is projected through the tubular crank case, but it has an external blister that is capable of accommodating the sweep of the elbow where the crank portion unites with the connecting shaft as the crank is projected through the crank casing. The invention will be clearly understood after reference to the following detailed specifications read in conjunction with the drawings.

In the drawings:

Figure I is a fragmentary view partially broken away showing a one piece crank being'inserted into the crank case according to the invention.

Figure II is a view showing the connecting portion of a three piece crank mounted in a crank casing according to our invention.

Figure III is a side view of the crank illustrated in Figures- I` and II, the dotted lines showing the position of the blister.

Figure IV is a cross sectional view of the crank case illustrated in Figures I, II and III.

Figure V is a side View of a conventional crank case for a three piece crank.

Referring to the drawings the tubular bicycle crank case I0 illustrated in Figures I to IV is constructed according to the invention. Its general geometry is similar to the geometry of prior I crank cases; by that we mean it has the usual sockets II, I2, I3 and I4 extending radially therefrom for connection with the usual bicycle frame members. This general geometry, and the manner in which the crank case is united to the tubular bicycle frame members, is so well-known that it need not further be expanded upon in this specication since the specification is concerned with the formation of the crank case per se and to include well-known bicycle construction would unnecessarily burden it.

Our crank case is designed to accommodate both a one piece bicycle crank illustrated fragmentarily in Figure I and generally referred to by numeral I5, the cross member I6 of the conventional three piece bicycle crank as indicated in Figure II, but the general diameter of the tubular crank case I0 is the size usually provided for the cross member I6 of the three piece crank.

As we have indicated above, the diameter of a tubular bicycle crank case for a one piece crank is customarily substantially greater than the diameter of a tubular crank case for a three piece crank because the one piece crank case must have a, suiiicient diameter to accommodate the sweep of the elbow I1 formed at the union of the crank arms I8 and the connecting shaft I9 of the one piece crank I5 when the crank is projected through the tubular crank case I IJ. The same diilculty does not arise lwith the conventional three piece crank because the crank arms are removed from the connecting portion IB before it is mounted in the crank case.

According to my invention we form the tubular crank case I of a bicycle frame with a crosssection too small to accommodate the sweep of the elbow` i7 of the one piece a'svity is projected through the tubular casing but also forni it with a blister 2i) that communicates with the interior of the crank case I0 to accommodate the sweep of the elbow l1 as the crank t5 isprojected through the crank casing for mounting.

By thus providing a blisteredgpntion; to amj commodate the elbow of the obie, 'bl to make a one piece crank case Illv capable of mounting a one piece crank that has the same general diameter as the diametex'oi the carmen` tional crank case for mounting the three piece crank. In Figure I, we have illustrated tht;l manL ner in which the one piece crank l5 is inserted for mounting in the crank case t0;

The practical advantages that from. this' are substantial because it is possible to mount in the one crank case either a. one piece. crank or a three piece crank It will beapparent that such a possibility will greatly simplify the. manufacture and servicing of bicycles.

The blister could be formed' in. a number of places, but we 'prefer to form it between the two connecting portions I3 and is, which", by those skilled in the art, wiliv be recognized. as the connecting portions that. unita with the lower rear forks in the bicycle frame, l

In Figure V we have shown 'a sideiview" of aconventional crank case 2l for a` three piece crank to illustrate the' sirnirarity in diameterv ci our improved crank case with iti Figures III and 1V are side views ofi 'our improved crank case drawn to the same scaleas the View ot Figure V'.

The only noticeablel difference'v is', perhaps, the

slight elongation of the' connecting members I3 and. M.

As we indicated above, our drawings have omitted all unnecessarl;x detail, Asvwell asomitting to snow a complete bicycle frame,v we have omitted tb show the complete crank t5;y the crank arms and their manner of connection for shaft L'G- of the three' piecey crank; and the 4siii-icificv jour-f nailing ineaiis for' the. cranks the crankcases-i All of these things are conventional, though, and very well known in the art and accordingly their omission is thought proper.

What we claim as our invention is:

1. In a bicycle. a tubular crank case, a onepiece crank having two crank arms with their longitudinal aires' in parallel spaced relation and united at their inner ends by a connecting shaft portion, said arms extending in opposite directions fro-m their points of union with said connecting shaft portion, said points of union hereinafter' being called elbows, an external blister formed in the wall of said crank case at one portion the wall of said crank case being too confining to hermit the elbow of said crank to pass therethrough save only at said portion where said blister is formed therein, said blister being elongated, the longitudinal axis of said blister being substantially parallel with the longitudinal axis of said tubular crank case, and having dimensions to accommodate one or said elbows 0i saidcrank. as it passes through said crank case, said blister having a width not subd stantially greater than the thickness of the crank.

2. In a. bicycle', a tirdm'larr crank case as claimed in ci'aini- 1,. haring sockets extending therefrom, to which are connected bicycle frame. members, two of. saidv sockets being' spaced apart for connection with rear fork members, said two latter sockets extending from said blister' and being aligned; longitudinally of said crank. case,

LEONARD SHAKESBY.. F. L. SAINSBURY.

References Cited in the le 0f this patenty STATES PATENTS Niiribe'r` Name Date 588,804 Iarish Y Y Aug. 24, 1897 672,135 Richards Apr.. 16,V 190i 2,353,712 Dewey July I8, 1944 FOREIGN PATENTS' Number i Conntry Date 11456117- Great Britain of 1893 461,725 Italy Feb. 9, i951 svg-,4ta Great Britain Aug. 1, i945 

